1. Technical Field
The present invention relates to pellets for shotgun ammunition and, more particularly, to metal combinations for such pellets which are non-toxic yet have specific gravities which are comparable to conventional toxic lead pellets, are safe to reload, and minimize damage to the barrel of a shotgun.
2. Discussion of the Prior Art
There has been considerable commentary in the literature concerning the problem of lead poisoning in waterfowl. Specifically, ducks and geese, as they feed along coastal regions, often swallow and ingest spent lead shot pellets. The ingested pellet or pellets are conveyed with other swallowed food and material to the bird's gizzard which grinds up the material as the first step in the digestion process. The lead pellet is eroded and provides a soluble lead salt that is passed into the digestive system. It has been found that the lead salt causes severe anemia and significantly limits the ability of the bird's blood to provide oxygen and nutrition to the body, resulting in a loss of appetite that weakens the bird to the point where it eventually dies or is eaten by a predator. Consequently, lead shot has been prohibited in certain areas of the United States.
The only commercially available alternative to lead shot at the present time is steel shot. There are, however, three significant problems associated with steel shot. One of these problems derives from the low specific gravity of steel, namely 7.9 g/cc, relative to the 11.3 g/cc specific gravity of lead. This lower density or specific gravity results in a lower kinetic energy and concomitant reduced killing power for steel than for lead for a given diameter and configuration of pellet. This fact is illustrated in FIG. 1 of the accompanying drawing wherein kinetic energy of a pellet versus distance of shot trajectory is graphically shown for two sizes of pellets, namely #2 steel and #2 lead or lead equivalent, and #4 steel and #4 lead, or lead equivalent. For example, at forty yards using #2 size shot, the lead shot has 8.2 ft/lbs of kinetic energy whereas the steel shot has only 5.8 ft/lbs, an energy difference of approximately thirty percent. If an arbitrary energy level (e.g., 2.5 ft/lbs) is established at which a shot pellet will clearly kill a bird rather than merely cripple it, it is clear from FIG. 1 that the #4 steel shot would be ineffective beyond forty-eight yards, whereas the #4 lead shot would effect a clean kill at up to sixty yards. The foregoing compares steel with pure lead; however, it should be noted that most "lead" shot sold commercially is actually ninety-four percent lead (Pb), by weight, and six percent antimony (Sb) by weight, resulting in a specific gravity of 11.1 g/cc. This small difference in density does not affect the foregoing analysis.
In order to compensate for this problem, manufacturers of steel shot recommend that waterfowl hunters use steel shot that is two sizes larger than the lead shot they would normally use. In other words, the larger size pellets have greater mass and therefore have higher kinetic energy. For example, if a hunter uses #6 lead shot for duck hunting, #4 steel shot would be recommended as a replacement. However, there are fewer pellets of the #4 steel shot than in the #6 lead shot resulting in a relatively low pattern density (i.e., number of pellets per unit area) at a range of sixty yards. In this regard, denser pellet patterns result in clean kills whereas the less dense patterns tend only to cripple. From a humane approach, the less dense patterns are obviously undesirable.
A second problem associated with steel shot is that components and data for reloading steel pellets into shot shells are not currently available to the hunter. The personal reloading of one's own shotshells is a widely practiced craft among American waterfowl hunters. In addition to the absence of reloading data for steel, there can be a safety problem in improperly reloading the steel shot. Since steel does not deform at all, it requires a slow-burning powder to prevent build-up of excessive gun chamber pressure. Therefore, gun chamber explosions can occur from incorrect loading.
A third problem associated with steel shot arises when the steel pellets are shot through a chromium or steel shotgun barrel. The steel pellets tend to wear the barrel, particularly the choke. It is far more desirable, therefore, to have shot pellets which are made of a softer and more malleable metal so as not to wear and erode the barrel.
Basically, there are three approaches to solving the problem of lead poisoning in waterfowl. These are: (1) providing a disintegratable lead shot which would fragment in water and thus become unavailable for ingestion; (2) coating the pellet to prevent absorption of ingested pellets into the system; and (3) replacing the lead with a less toxic metal or alloy. Disintegratable lead shot suffers from storage problems in that moisture tends to cause premature disintegration. Further, the trajectory characteristics of such shot are erratic. On the other hand, coating the pellets has proven to be ineffective as the coating quickly is abraded away in the gizzard environment.
Replacement metals and alloys have met with little success in the prior art. For example, in U.S. Pat. No. 1,703,577 (Falkenberg), a technique is described whereby metallic tungsten (W) is dissolved in alloys of lead and antimony, or in alloys of zinc, lead and iron (Fe). There is no discussion in the patent of any relationship between specific gravity and kinetic energy, and no reference to toxicity. Permissible lead content of the alloy ranges up to eighty percent by weight which is far beyond the maximum of approximately forty percent required to avoid toxicity.
In U.S. Pat. No. 2,167,828 (Dowdel et al), a technique is described for reducing lead poisoning in waterfowl by alloying small amounts of either magnesium, zinc, lithium, sodium, barium, potassium or calcium with lead (approximately ninety-six percent lead). These minor additives are provided for the express purpose of hastening the decomposition of the lead alloy in aqueous solution. The patent also describes a copper coating for preventing the same decomposition in a bird's "moist flesh". The resulting alloy, however, is still highly toxic due to the relatively high lead content.
U.S. Pat. No. 3,363,561 (Irons) discloses a shot gun pellet constructed of an iron core with numerous optional plastic coatings for reducing barrel wear. The resulting pellet has considerably lower specific gravity than a lead pellet.
In U.S. Pat. No. 3,900,317 (Meadus et al), a process for forming shot using iron, lead, tin (Sn), copper and zinc is described. However, powder metallurgy is employed whereby sintered composite powders are packed in graphite and sintered at about 1,000.degree. C. Typically, the alloys described have specific gravities on the order of 7.5 g/cc which is not an improvement, even with respect to steel shot. Moreover, the fifty-five percent by weight content of lead is considered toxic to waterfowl. The complicated and expensive powder metallurgy process, and lack of alloy density, preclude commercial viability of the alloy.
U.S. Pat. No. 4,383,853 (Zapffe) discloses a technique whereby depleted uranium is alloyed with iron and chromium at a temperature below 1535.degree. C. Although uranium and its salts are quite toxic, it is stated in the patent that chromium will render the uranium harmless by forming a "stainless steel-like matrix". These alloys require high temperature to fabricate and result in an associated high energy cost. The alloys also achieve a specific gravity of 8.4 g/cc, which is only seventy-four percent of that of lead. No mention is made in the patent of hardness of the material or of potential shotgun wear, but if the alloy lies midway in the stated concentration ranges, it should have a hardness of 400 brinell, or greater, and would definitely cause barrel erosion.
Finally, the cost of the individual elements must be given over-riding consideration in formulating any alloy, including alloys utilized in forming shotgun pellets.